Lanthanum cobalt oxide La2CoO4 exhibits unusually fast oxygen transport in the spontaneous intercalation of molecular oxygen at ambient temperature. The present work concerns investigations on the mechanism of the chemical and electrochemical intercalation process. It is shown that two nonstoichiometric phases and one line phase are formed as intermediates with different kinetics. Carbon dioxide was found to be an efficient inhibitor for the O-2 uptake reaction. Several models are discussed in order to explain the phenomenon of fast oxygen anion transport at low temperatures.